Chuck with torque limiting mechanism and inclined plane for final tightening

ABSTRACT

A chuck for releasably holding a tool such as a drill bit has a torque limiting coupling in the mechanism which is rotated manually to close the jaws of the chuck on the tool. When the chuck has been tightened on the tool by a certain amount, the torque limiting coupling releases. Thereafter, continued manual rotation of the component which provides the input to the coupling operates a cam and cam follower mechanism which forces the jaws of the chuck into even tighter engagement with the tool. When the chuck is subsequently loosened to release the tool, the cam and cam follower mechanism automatically resets to ready the chuck for reuse.

BACKGROUND OF THE INVENTION

This invention relates to chucks for releasably holding tools (e.g.,drill bits), and more particularly to such chucks which can be easilyand simply operated to very securely hold a tool without the need for akey to tighten the chuck on the tool.

Chucks with keys for imparting final tightening torque to the chuck tosecurely hold a tool are well known. While such chucks have been highlysuccessful, they may have certain disadvantages. For example, the keymust be removed from the chuck before the chuck is rotated at high speed(e.g., in a drilling operation). Failure to remove the key may unbalancethe chuck when rotated at high speed, or cause the key to be thrown outfrom the chuck in a radial direction in a possibly unsafe manner.Although the key must thus be frequently removed from the chuck, the keymust somehow be kept with the chuck or it may become lost.

Because of these disadvantages of keyed chucks, there has beenincreasing interest in recent years in chucks which can be operated byhand without the need for keys (see, for example, Huff et al. U.S. Pat.No. 5,125,673 and Jordan et al. U.S. Pat. No. 5,215,317). Some of thesekeyless chucks have been highly successful, but there is always room forfurther improvement.

To be acceptable a chuck must be able to hold a tool very securely.Chuck jaws with relatively fine threads serve this objective becausefine threads give increased mechanical advantage. However, fine threadsmake a chuck relatively slow to operate, thereby making the chuckobjectionable or even unacceptable to some users. A chuck should also beas simple and easy to operate as possible. For example, it is preferablefor the operator to be able to use a single, simple type of motion totighten or loosen the chuck. The chuck should also reset reliably andautomatically after each use so that no additional resetting operationis required from the operator.

In view of the foregoing, it is an object of this invention to provideimproved chucks.

It is another object of this invention to provide manually operable,keyless chucks which do not require especially fine jaw threads to holda tool very securely, indeed more securely than conventional keylesschucks with fine threads.

It is still another object of this invention to provide manuallyoperable, keyless chucks which require the operator to perform only asingle, straightforward motion to tighten or loosen the chuck, and whichautomatically reset after each use in a highly reliable manner.

SUMMARY OF THE INVENTION

These and other objects of the invention are accomplished in accordancewith the principles of the invention by providing a chuck with a torquelimiting mechanism between (1) the chuck component (typically a sleeve)which is manually rotated to tighten the chuck on a tool and (2) thechuck component (typically a nut) which is rotated by the sleeve toadvance the jaws of the chuck to grip the tool. When the jaws have beentightened on a tool to a predetermined degree, the resistance to furthertightening causes the torque limiting mechanism to release. This allowsthe sleeve to rotate relative to the nut. The above-described initialtightening of the jaws on the tool also compresses a plurality ofrolling cam follower elements (e.g., ball bearings) between aproximal-facing surface of the nut and a distal facing surface whichrotates with the sleeve. When the sleeve rotates relative to the nut,the cam follower elements roll along segments of the surfaces betweenwhich the cam follower elements are compressed. These segments on atleast one of the surfaces are inclined toward the other surface in thedirection in which the cam follower elements roll so that the camfollower elements force the nut axially forward relative to the body ofthe chuck as the cam follower elements roll. This forward motion of thenut forces the jaws farther forward, thereby providing final tighteningof the chuck jaws on the tool.

When the chuck is again loosened, the cam follower elements are nolonger axially compressed between the surfaces along which they roll asdescribed above. A relatively light spring is therefore effective toautomatically restore the cam follower elements to their initialpositions relative to the inclined surface segments along which theyroll.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevational view, partly in section, of an illustrativechuck constructed in accordance with the principles of this invention.

FIG. 2 is a partial sectional view taken along the line 2--2 in FIG. 1.

FIG. 3 is an elevational view of one part of the chuck of FIG. 1 takenin the direction of arrows 3 in FIG. 1.

FIG. 4 is a partial sectional view taken along the line 4--4 in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a chuck 10 constructed in accordance with theprinciples of this invention has a main body 20 with a centrallongitudinal bore 22 and three subsidiary bores 24 spaced equidistantlyfrom one another around the central longitudinal axis 12 of the chuck.(Only one of bores 24 is visible in FIG. 1.) The proximal (right-most)end of bore 22 is adapted to receive a driver for the chuck (e.g., theend of the shaft of a manual or powered drill). Bores 24 are inclinedtoward one another in the distal direction (toward the left) andcommunicate with the distal portion of bore 22.

A longitudinal jaw 30 is disposed in each of bores 24. Each of jaws 30is reciprocable along its longitudinal axis 32. Jaws 30 are reciprocatedby nut 40, which is rotatably mounted on body 20 concentric with axis 12and threadedly engaged with each of jaws 30. Rotation of nut 40 relativeto body 20 therefore causes jaws 30 to move in unison, either toward oraway from axis 12, depending on the direction of rotation of the nut.Nut 40 is rotated by rotation of annular front sleeve 50 which (like nut40) is rotatably mounted on body 20 concentric with axis 12. In general,torque is transmitted from sleeve 50 to nut 40 by ring 60 which isdisposed between elements 40 and 50 concentric with axis 12. Theconstruction and operation of ring 60 are described in more detailbelow.

Behind nut 40 (in the proximal direction) is a plurality of ballbearings 70 spaced from one another in an annular array concentric withaxis 12 by being disposed in similarly spaced apertures in cage ring 72(see also FIG. 4). In the particular embodiment shown in the drawingsthere are four balls 70 equally spaced from one another around axis 12.Behind ball bearings 70 (again in the proximal direction) is an annularcam ring 80 which is concentric with axis 12. Cam ring 80, which isanother part that is described in more detail below, is constrained torotate with sleeve 50 at all times by lugs 52 on sleeve 50 projectingradially inward into mating notches 82 (FIG. 3) in cam ring 80.

Behind cam ring 80 (in the proximal direction) is another ball bearingstructure including a plurality of ball bearings 90 spaced from oneanother in an annular array concentric with axis 12 by cage ring 92.(Cage ring 92 is optional and can be omitted if desired.) In theproximal direction ball bearings 90 bear on annular bearing race 100 onbody 20. A rear sleeve 110 is secured to the rear of body 20. Nose piece120 is pressed onto the distal end of body 20 and thereby holds elementssuch as 40, 50, and 60 on body 20. However, limited motion of nut 40parallel to axis 12 is permitted.

The construction of ring 60 and associated parts is shown in more detailin FIG. 2. Ring 60 has a pair of diametrically opposite, radially andaxially extending lugs 62, each of which projects radially inward into amating axially extending channel 42 in nut 40. Nut 40 and ring 60 arethereby constrained to rotate with one another at all times. Ring 60also has a pair of diametrically opposite, radially and axiallyextending lugs 64 which project radially outward from its outer surface.Each of lugs 64 has a substantially radial face 64b and a generallyopposite inclined face 64a. Radially inside each of lugs 64 ring 60 hasa circumferentially and axially extending aperture 66 which allows theadjacent lug 64 to move radially inward under certain conditions asdescribed below.

Lugs 64 on ring 60 interdigitate with radially and axially extendinglugs 54 on sleeve 50. Lugs 54 are diametrically opposite one another andproject radially inward from the sleeve. Like lugs 64, each of lugs 54has a substantially radial face 54b and a generally opposite inclinedface 54a. When sleeve 50 is rotated in the direction indicated by arrow56 in FIG. 2 (which is the direction of sleeve rotation required totighten jaws 30 on a tool), sleeve 50 can rotate relative to nut 40until the inclined surfaces 54a of lugs 54 contact the inclined surfaces64a of lugs 64. Thereafter, continued rotation of sleeve 50 in direction56 causes ring 60 and therefore nut 40 to rotate in direction 56. Thiscauses jaws 30 to move in the distal direction until the tool is grippedby the laws.

When jaws 30 contact the tool, it becomes increasing difficult tocontinue to rotate nut 40 in direction 56 as the tool gripping forceexerted by the jaws increases. It should also be noted that anotherconsequence of the gripping force exerted by jaws 30 on the tool is areaction force which causes nut 40 to move in the proximal direction andapply a compressive force to balls 70, cam ring 80, and balls 90. Whenthe manual torque which must be applied to sleeve 50 to continue torotate nut 40 in direction 56 reaches a predetermined threshold torque,ring 60 flexes inwardly in the vicinity of lugs 64 and apertures 66,thereby allowing each of lugs 54 to pass the lug 64 with which it wasformerly in contact. The structure thus described therefore acts as adetent-type torque limiting mechanism. When the detent of this torquelimiting mechanism releases, sleeve 50 can continue to rotate indirection 56 without further rotating ring 60 or nut 40. Cam ring 80,however, continues to rotate in direction 56. And because balls 70 havebeen compressed between nut 40 and cam ring 80, balls 70 begin to rollalong the mutually opposing faces of non-rotating nut 40 and rotatingcam ring 80. As balls 70 thus roll, they carry cage ring 72 with them.In particular, it will be noted that during this phase of the operation,cage ring 72 rotates about axis 12 in direction 56 at one-half the speedat which sleeve 50 and cam ring 80 are rotating. Springs 130, which asbest seen in FIG. 4 extend between sleeve 50 and cage ring 72, arestretched (i.e., placed in increasing tension) by this rotation ofsleeve 50 relative to cage ring 72.

As shown in FIG. 3, the surface of cam ring 80 along which balls 70 rollas described above has four arcuate channels 84 spaced from one anotheraround the cam ring. Each of balls 70 rolls in a respective one ofchannels 84. These channels have cross sections which are concave tocomplement the convex outer surfaces of balls 70. Each of channels 84becomes gradually shallower in the direction opposite direction 56.Accordingly, as cam ring 80 rotates relative to nut 40 in direction 56,each ball 70 rolls from the deeper end 84a of the associated channeltoward the shallower end 84b of that channel. Cam ring 80 thereby forcesballs 70 to move in the distal direction. Balls 70 in turn force nut 40and jaws 30 to move in the distal direction, thereby significantlytightening the grip of jaws 30 on the tool being held by the chuck. Theextreme shallow end 84b of each channel 84 may be slightly deeper thanthe immediately adjacent portion of that channel so that the associatedball 70 has a tendency to remain at the shallow end of the channel untilthe chuck is deliberately loosened by turning sleeve 50 opposite todirection 56 as described in detail below.

From the foregoing it will be seen that the bottom of each channel 84 isa ramp, inclined plane, or cam surface, with the associated ball 70 as arolling follower for transmitting its axial motion as a follower to nut40 and therefore to jaws 30. The slope of each channel 84 is extremelygradual, so that very large mechanical advantage is developed from therotation of sleeve 50 relative to nut 40 during operation of cam ring 80in the manner just described. It will be noted that each channel 84subtends an angle of about 70°. Sleeve 50 therefore rotates in direction56 through an angle of about 140° in order to roll balls 70 from thedeeper ends 84a of channels 84 to the shallower ends 84b of thechannels. Because lugs 54 are about 180° apart on sleeve 50 and lugs 64are about 180° apart on ring 60, after lugs 54 and 64 pass one anotherto initiate the rolling of balls 70, the balls reach the shallow ends84b of channels 84 before lugs 54 re-engage lugs 64.

When it is desired to loosen the chuck and remove the tool held by jaws30, sleeve 50 is rotated opposite to direction 56. This causes balls 70to roll back from the shallow ends 84b of channels 84 to the deeper ends84a of those channels, thereby relieving some of the pressure of jaws 30on the tool. As balls 70 approach the deeper ends of channels 84, theradial faces 54b of lugs 54 come into contact with the radial faces 64bof lugs 64. As a result of this contact, continued rotation of sleeve 50opposite to direction 56 causes ring 60 and nut 40 to rotate opposite todirection 56. This retracts jaws 30 and releases the tool from thechuck. When the pressure of the jaws on the tool is sufficientlyrelieved, elements 70, 80, and 90 are no longer compressed between nut40 and bearing race 100. This allows springs 130 (acting in tension inthe circumferential direction between sleeve 50 and ball cage 72) toautomatically rotate ball cage 72 (if necessary) relative to elements 50and 80 so that balls 70 return to the deeper ends 84a of channels 84.The chuck is thus fully and reliably reset after each use so that it isalways ready for the next use. Because springs 130 are only required torotate cage ring 72 when there is substantially no compressive force onballs 70, the force of springs 130 can be relatively small so that evenwhen they are fully stretched, they do not significantly tend to loosenthe tightened chuck by strongly urging balls 70 to roll from the shallowends 84b of channels 84 to the deeper ends 84a of those channels.

When it is next desired to clamp a tool in the chuck, sleeve 50 is againrotated in direction 56. The first nearly 180° of this rotation may berequired to cause the inclined surfaces 54a of lugs 54 to re-engage theinclined surfaces 64a of lugs 64. (Balls 70 do not roll during thisrelative rotation between sleeve 50 and nut 40 because balls 70 are notthen compressed between the nut and ring 80.) Thereafter, continuedrotation of sleeve 50 in direction 56 rotates ring 60 and nut 40 in thesame direction, thereby moving jaws 30 in the distal direction towardthe tool to be clamped. Operation of the chuck then continues as firstdescribed above.

Among the advantages of chuck 10 is that sleeve 50 is substantiallydecoupled from nut 40 while the chuck is tightened on a tool. Theinertia of nut 40 is thereby reduced. This enhances the ability of thechuck to remain tight by resisting vibration and accelerations in thelongitudinal and circumferential directions.

Although the various components of chuck 10 can be made of any of manysuitable materials, particularly preferred materials for sleeve 50 andring 60 are nylon and acetal, respectively.

It will be understood that the foregoing is only illustrative of theprinciples of this invention, and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention. For example, the numbers of such components as lugs54, lugs 64, balls 70, and channels 84 can be varied as desired. If thechuck is mounted on a tool having a spindle lock, sleeve 50 can beextended farther to the rear and separate rear sleeve 110 can beeliminated. As another example of possible modifications, channels 84can be moved from the distal surface of ring 80 to the oppositeproximal-facing surface of nut 40, or such inclined channels can beprovided on both of these surfaces. Radially extending roller bearingsmay be used in place of balls 70, with appropriate modification of theshape of channels 84 to accept such rollers rather than balls. Insteadof having lugs 64 deflect inwardly to pass lugs 54, lugs 54 coulddeflect outwardly to permit such passing. Instead of having stopsurfaces 54b and 64b which are positioned to engage one another beforesleeve 50 is rotated all the way back to the position in which theassociated inclined surfaces 54a and 64a are facing one another, lugs 54and 64 could be shaped so that they very easily pass one another whensleeve 50 is rotated in the loosening direction, and other stop surfaces(like surfaces 54b and 64b but with at least different angular positionsand possibly also different axial positions) could then engage oneanother to prevent further rotation of sleeve 50 opposite to direction56 without similar chuck-loosening rotation of ring 60 and nut 40.Indeed, these alternative stop surfaces could be located on elementsother than 50 and 60 if desired. As still another example of possiblemodifications, the torque limiting operation provided between sleeve 50and ring 60 could alternatively be provided between ring 60 and nut 40.Instead of the releasable detent-type torque limiting mechanism shown inthe drawings, the torque limiting mechanism could be of the frictiontype. Such a friction-type torque limiting mechanism takes advantage ofthe fact that static friction between two surfaces is greater thansliding friction between those surfaces under otherwise similarconditions. Thus static friction between elements 50 and 60 would beused to transmit torque from sleeve 50 to ring 60 until a thresholdtorque was reached, at which point reduced sliding friction would allowsleeve 50 to rotate relative to ring 60.

It will be noted that the torque limiting mechanisms employed inaccordance with this invention are preferably "passive" in the sensethat they do not store energy to any significant degree. This is true ofboth the depicted releasable detent-type torque limiting mechanism andthe alternative friction-type torque limiting mechanism describedimmediately above. These passive torque limiting mechanisms transmittorque applied to them, but unlike a spring, for example, they do notsignificantly store energy which could cause the chuck to loosen afterit has been tightened on a tool and while the tool is being used.

The invention claimed is:
 1. A chuck for releasably gripping a toolcomprising:a main body; a plurality of longitudinal tool-gripping jawsmounted for movement relative to said main body, each of said jaws beingmovable relative to said main body parallel to a longitudinal axis ofthat jaw, the longitudinal axes of said jaws being synclinal in a distaldirection along said body; a nut rotatably mounted on said body, saidnut being also mounted for limited axial motion relative to said bodyparallel to said distal direction, said nut being threadedly engagedwith each of said jaws for causing said jaws to move parallel to theirlongitudinal axes when said nut is rotated relative to said body or whensaid nut is moved axially relative to said body parallel to said distaldirection; a sleeve rotatably mounted on said body; a torque limitingcoupling operatively connected between said sleeve and said nut forcausing said nut to rotate relative to said body with said sleeve in ajaw-tightening direction until said jaws have begun to grip said tooland more than a predetermined threshold torque must be applied to saidsleeve to continue to rotate said nut in said jaw-tightening direction,after which said torque limiting coupling releases so that said sleevecan continue to rotate in said jaw-tightening direction with at leastsubstantially reduced transmission of torque from said sleeve to saidnut and therefore without further rotation of said nut in saidjaw-tightening direction, said predetermined threshold having a valuegreater than a minimum required to couple said sleeve and said nutbefore said jaws grip said tool and substantially less than a valuerequired to finally tighten said tool for operation; a plurality ofrolling cam follower elements disposed between a substantiallyproximal-facing first surface of said nut and a substantiallydistal-facing second surface that rotates relative to said body withsaid sleeve, said cam follower elements being axially compressed betweensaid first and second surfaces only after said jaws have begun to gripsaid tool and said nut moves relative to said body in the proximaldirection in reaction to the tool-gripping force applied to said tool bysaid jaws, each of said cam follower members rolling, from initialpositions relative to said first and second surfaces, along an arcuatesegment of each of said first and second surfaces when said cam followerelements are compressed between said first and second surfaces and aftersaid torque limiting coupling has released and said sleeve continues torotate in said jaw-tightening direction relative to said nut, at leastone of said segments along which each of said cam follower elementsrolls being inclined toward another of the segments along which that camfollower element rolls in the direction in which that cam followerelement rolls so that said cam follower elements force said nut to movein said distal direction relative to said body, thereby furthertightening said jaws on said tool; and means for resiliently urging eachof said cam follower elements to automatically return to its initialposition relative to at least one of said first and second surfaces whensaid cam follower elements are not compressed between said first andsecond surfaces.
 2. The apparatus defined in claim 1 wherein said camfollower elements are connected to one another by an annular cage ringwhich is disposed circumferentially around said body and which isrotatable relative to said body and relative to said first and secondsurfaces, and wherein said means for resiliently urging comprises aspring which acts in the circumferential direction between said cagering and at least one of said first and second surfaces.
 3. Theapparatus defined in claim 1 wherein said torque limiting couplingcomprises a releasable detent coupling between said sleeve and said nut,said releasable detent coupling transmitting torque from said sleeve tosaid nut when said sleeve is rotated in said jaw-tightening directionuntil said torque reaches said threshold torque, after which saidreleasable detent coupling releases and transmits substantially notorque from said sleeve to said nut during continued rotation of saidsleeve in said jaw-tightening direction.
 4. The apparatus defined inclaim 1 wherein each of said cam follower elements is a ball.
 5. Theapparatus defined in claim 4 wherein at least one of said segments alongwhich each of said balls rolls is a channel having a concave crosssection for receiving a portion of the surface of said ball.
 6. Theapparatus defined in claim 5 wherein each of said channels becomesprogressively shallower in the direction in which the ball in saidchannel rolls.
 7. The apparatus defined in claim 1 furthercomprising:stop means operatively coupled between said sleeve and saidnut for preventing said sleeve from rotating by more than apredetermined amount relative to said nut in a direction opposite tosaid jaw-tightening direction.
 8. The apparatus defined in claim 1wherein each of said segments along which said cam follower elementsroll is an arc substantially concentric with an axis about which saidnut concentrically rotates.